An international research team has developed an electrically-pumped continuous wave semiconductor laser suitable for seamless silicon integration. According to the team, this is the first laser of its kind directly grown on a silicon wafer. Developed by scientists from Forschungszentrum Jülich (FZJ), the University of Stuttgart, and the Leibniz Institute for High Performance Microelectronics (IHP), together with CEA-Leti, the laser is composed exclusively of elements from the fourth group of the periodic table — the “silicon group.” Built from stacked ultrathin layers of germanium-tin and silicon germanium-tin, the device opens new possibilities for on-chip integrated photonics, the researchers said. An international research team developed an electrically-pumped germanium-tin laser grown on silicon. The development marks the first efficient, electrically pumped light source made with Group IV semiconductors, the team said. Courtesy of Forschungszentrum Jülich/Jhonny Tiscareno. The laser addresses the lack of an efficient, electrically-pumped light source using only Group IV semiconductors. Monolithic integration of optically active components on silicon chips has traditionally been done with III-V materials, which are difficult and expensive to integrate with silicon. In an optically pumped laser, an external light source is required to generate the lasing light, while the electrical pumped laser generates light when an electrical current is passing through the diode. Electrically pumped lasers are usually more energy efficient, because they directly convert electricity into laser light. The laser developed by the researchers is compatible with the conventional CMOS technology for chip fabrication and is therefore suitable for seamless integration into existing silicon manufacturing processes. According to the researchers, it could therefore be seen as the “last missing piece” in the silicon photonics toolbox. A schematic view of the newly-developed germanium-tin laser. Courtesy of Forschungszentrum Jülich/Jhonny Tiscareno. According to Dan Buca of FZJ’s Peter Grünberg Institute, the development has been one of the main goals of his group’s exploration of germanium-tin alloys, work that has been ongoing for almost a decade. Unlike previous germanium-tin lasers that relied on high-energy optical pumping, this new laser operates with a low current injection of just 5 mA at 2 V, comparable to the energy consumption of a light-emitting diode. With its advanced multiquantum well structure and ring geometry, the laser minimizes power consumption and heat generation, enabling stable operation up to 90 K or -183.15 C. Grown on standard silicon wafers like those used for silicon transistors, it represents the first truly “usable” Group IV laser, though additional optimizations are needed to further reduce the lasing threshold and achieve room-temperature operation. However, the success of earlier optically pumped germanium-tin lasers, which have evolved from cryogenic to room-temperature operation in only few years, suggests a clear path forward. The research was published in Nature Communications (www.doi.org/10.1038/s41467-024-54873-z).